The present invention relates generally to electronic article security (EAS) systems for detecting the presence of a security tag within a security zone and more particularly to an improved electronic article security system having the capability for localizing a resonant security tag within a portion of the security zone.
The use of electronic article security systems for detecting and preventing theft or unauthorized removal of articles or goods from retail establishments and/or other facilities such as libraries has become widespread. In general, such EAS systems employ a security tag, which is detectable by the EAS system and which is secured to the article to be protected. Such EAS systems are generally located at or around points of exit irom such facilities to detect the security tag, and thus the article, as it transits through the exit point.
Due to environmental and regulatory considerations, individual EAS systems are generally effective over only a limited area in which a security tag attached to a protected article may be reliably detected. Such area, typically referred to as a security zone, is generally limited to about six feet in width for a single EAS system. While many stores and libraries have only a single exit doorway of a size commensurate with such a six foot wide security zone, many other retail establishments have eight or ten exit doorways arranged side by side. Furthermore, large mall stores frequently have a generally wide open area or aisle of ten feet or more in width serving as a connection with the mall. Thus, in many such situations, a plurality of EAS systems are required to fully protect exit/entrance points having a width greater than that which can be reliably protected by a single EAS system.
In a large mall entryway that needs to be protected, it is likely that the store owner will not want to employ a traditional EAS system installation which would include multiple, large, side-side "pedestal" antenna structures, due to aesthetic visual or marketing reasons. Such store owners would prefer an "invisible" EAS system in which the EAS antenna structure is mounted in the floor beneath the entryway, hung over the entryway or both. Such EAS systems usually provide adequate detection of tagged merchandise transiting through the security zone but fail to provide a localization of a detection to a specific portion of the security zone. Thus, when many customers are in proximity of the entryway when an alarm is activated, store personnel generally have no way, other than trial and error, to determine which customer has set off an alarm with the tagged merchandise. This leads to either a lack of use of the EAS system as an effective security aid, or the owner having disgruntled customers who take their business elsewhere.
The present invention overcomes the problem of an "invisible" EAS system not being able to localize a tag detection to a specific portion of the security zone in a large entryway by utilizing a plurality of EAS sensors of the pulse-listen type, in combination with a plurality of antennas placed either above or below the entryway. The resulting EAS system determines the relative proximity of a detected security tag transiting through the security zone to each of the plurality of antennas in the array. The resulting EAS system achieves localization of a security tag to within a small portion of the security zone.